The rule of thumb in all these cases is to stick to the basics no matter what. Tell me a story about a guy who...

I can identify with.
I can learn from.
I have compelling reason to follow.
I believe deserves to win and...
Has stakes that are primal and ring true for me.

Follow that simple prescription for finding the hero of your movie and you can't go wrong. No matter what assignment, material, or sweeping canvas has been handed to you, you find the hero by finding the heart of the story.